FIGS. 1-3 illustrate a prior art rear door frame 200 for a trailer. The rear frame 200 forms a rectangular opening into which the rear doors (not shown) are provided. The rear frame 200 includes an elongated horizontal sill 202, a pair of vertical posts 204 (only one of which is shown) that extend upwardly from the opposite ends of the sill 202, and an elongated horizontal top member (not shown). The posts 204 are connected to the sidewalls of the trailer by known means; the opposite ends of the sill 202 are connected to the baserails of the trailer by known means; and the opposite ends of the top member are connected to the top rails of the trailer by known means. A bumperette 205 is attached to the outer surface of each post 204.
The prior art sill 202 is formed from a fantail 206 and a flat base plate 208. The fantail 206 is formed as a channel and has a vertical rear wall 210, a vertical front wall 212 and a top wall 214 which connects the upper ends of the rear and front walls. The top wall 214 is formed of a rear wall portion 216 which is connected to the upper end of the rear wall 210, a front wall portion 218 which is connected to the upper end of the front wall 212, and a vertical wall 220 which connects the rear wall portion 216 to the front wall portion 218. The front wall portion 218 is stepped downwardly from the rear wall portion 216. This results in an open cross-section of the sill 202 which is rigid in bending, but not in torsion. In addition, the rear sill 202 is relatively large, having a vertical dimension along the rear wall 210 of 8.5 inches and a horizontal dimension along the top wall 214 of 8.19 inches.
The base plate 208 is attached to the bottom end of the rear wall 210 of the fantail 206, to the underside of each post 204 and to the underside of each bumperette 205. Along the rear of the trailer, the base plate 208 extends outwardly from the rear end of the fantail 206.
During assembly of the trailer in the manufacturing facility, a pair of bumper brackets 222 (only one of which is shown) are attached to the fantail 206 by welding. Each bracket 222 has a vertical front wall 224 which is attached to the front wall 212 at its upper end, and a horizontal bottom wall 226 extending from the bottom end of the front wall 224 toward the rear end of the trailer. A wall 228 closes the sides of the front and bottom walls 224, 226 and abuts against the rear wall 210. A notch 232 is formed in the wall 228 and the flat base plate 208 is seated within the notches 232.
During assembly of the trailer in the manufacturing facility, a standard bolt-on bumper 234 is attached to the bumper brackets 222. The bolt-on bumper 234 generally includes a pair of spaced apart vertical legs 236 (only one of which is shown) and a horizontal bumper 238 which is mounted to the lower ends of the legs 236. The legs 236 are attached to the bumper brackets 222.
The rear sill 202 of a trailer has to withstand large dynamic loads when a fork truck (e.g., with 24,000 lb front axle weight) enters the trailer at the dock, or when a trailer impacts a dock while backing up to the dock. These are large dynamic load that could potentially lead to fatigue cracking welded joints or even permanently bend the sill 202.
To attach a tuck-under lift gate, such as one sold by the Maxon or Leyman companies, the standard bolt-on bumper 234 and the bumper bracket 222 installed in the trailer manufacturing facility are removed, and the rear sill 202 is notched by the tuck-under lift gate installer to accommodate the legs of the lift gate in the raised position. A deck extension plate (not shown) may be attached to the rear wall 210 of the fantail 206 by suitable means, such as welding. The deck extension plate is relatively thin, generally ½ of an inch. The notching of the rear sill 202 to accommodate the tuck-under lift gate is undesirable as this may weaken the rear sill 202. Stress risers may form, thereby impacting the fatigue life, durability and safety of the sill 202. In addition, this requires additional time and effort to mount the tuck-under lift gate.
Thus, it is desirable to provide a trailer rear door frame that allows for installation of tuck-under lift gates from all major lift gate manufacturers in the United States without modification to the structure of the rear sill.